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Can the Synergic Contribution of Multigenic Variants Explain the Clinical and Cellular Phenotypes of a Neurodevelopmental Disorder?

ABSTRACT: We describe an infant female with a syndromic neurodevelopmental clinical phenotype and increased chromosome instability as cellular phenotype. Genotype characterization revealed heterozygous variants in genes directly or indirectly linked to DNA repair: a de novo X-linked HDAC8 pathogenic variant, a paternally inherited FANCG pathogenic variant and a maternally inherited BRCA2 variant of uncertain significance. The full spectrum of the phenotype cannot be explained by any of the heterozygous variants on their own; thus, a synergic contribution is proposed. Complementation studies showed that the FANCG gene from the Fanconi Anaemia/BRCA (FA/BRCA) DNA repair pathway was impaired, indicating that the variant in FANCG contributes to the cellular phenotype. The patient's chromosome instability represents the first report where heterozygous variant(s) in the FA/BRCA pathway are implicated in the cellular phenotype. We propose that a multigenic contribution of heterozygous variants in HDAC8 and the FA/BRCA pathway might have a role in the phenotype of this neurodevelopmental disorder. The importance of these findings may have repercussion in the clinical management of other cases with a similar synergic contribution of heterozygous variants, allowing the establishment of new genotype-phenotype correlations and motivating the biochemical study of the underlying mechanisms.

SUBMITTER: Maia N

PROVIDER: S-EPMC8774836 | biostudies-literature | 2021 Dec

REPOSITORIES: biostudies-literature

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Can the Synergic Contribution of Multigenic Variants Explain the Clinical and Cellular Phenotypes of a Neurodevelopmental Disorder?

Maia Nuno N Nabais Sá Maria João MJ Oliveira Cláudia C Santos Flávia F Soares Célia Azevedo CA Prior Catarina C Tkachenko Nataliya N Santos Rosário R de Brouwer Arjan P M APM Jacome Ariana A Porto Beatriz B Jorge Paula P

Genes 20211228 1

We describe an infant female with a syndromic neurodevelopmental clinical phenotype and increased chromosome instability as cellular phenotype. Genotype characterization revealed heterozygous variants in genes directly or indirectly linked to DNA repair: a de novo X-linked HDAC8 pathogenic variant, a paternally inherited FANCG pathogenic variant and a maternally inherited BRCA2 variant of uncertain significance. The full spectrum of the phenotype cannot be explained by any o ...[more]

PMID: 35052418

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Project description:BackgroundHeterozygous disruption of FOXP2 causes a rare form of speech and language impairment. Screens of the FOXP2 sequence in individuals with speech/language-related disorders have identified several rare protein-altering variants, but their phenotypic relevance is often unclear. FOXP2 encodes a transcription factor with a forkhead box DNA-binding domain, but little is known about the functions of protein regions outside this domain.MethodsWe performed detailed functional analyses of seven rare FOXP2 variants found in affected cases, including three which have not been previously characterized, testing intracellular localization, transcriptional regulation, dimerization, and interaction with other proteins. To shed further light on molecular functions of FOXP2, we characterized the interaction between this transcription factor and co-repressor proteins of the C-terminal binding protein (CTBP) family. Finally, we analysed the functional significance of the polyglutamine tracts in FOXP2, since tract length variations have been reported in cases of neurodevelopmental disorder.ResultsWe confirmed etiological roles of multiple FOXP2 variants. Of three variants that have been suggested to cause speech/language disorder, but never before been characterized, only one showed functional effects. For the other two, we found no effects on protein function in any assays, suggesting that they are incidental to the phenotype. We identified a CTBP-binding region within the N-terminal portion of FOXP2. This region includes two amino acid substitutions that occurred on the human lineage following the split from chimpanzees. However, we did not observe any effects of these amino acid changes on CTBP binding or other core aspects of FOXP2 function. Finally, we found that FOXP2 variants with reduced polyglutamine tracts did not exhibit altered behaviour in cellular assays, indicating that such tracts are non-essential for core aspects of FOXP2 function, and that tract variation is unlikely to be a highly penetrant cause of speech/language disorder.ConclusionsOur findings highlight the importance of functional characterization of novel rare variants in FOXP2 in assessing the contribution of such variants to speech/language disorder and provide further insights into the molecular function of the FOXP2 protein.

Dataset Information

Can the Synergic Contribution of Multigenic Variants Explain the Clinical and Cellular Phenotypes of a Neurodevelopmental Disorder?

Publications

Can the Synergic Contribution of Multigenic Variants Explain the Clinical and Cellular Phenotypes of a Neurodevelopmental Disorder?

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